The RCCX region has multiple pseudogenes and tandem repeat sequences that promote misalignment during meiosis leading to complex gene rearrangements, deletions and gene conversion events. CYP21A2 mutations cause Congenital Adrenal Hyperplasia (CAH) and TNX deficiency has been proposed as a cause of hypermobile Ehlers Danlos syndrome (EDS). The structure of the RCCX module in a cohort of patients with CAH seen at the National Institute of Child Health and Development under Protocol 06CH001, and in patients with EDS seen at the National Institute on Aging under protocol 2003-086 has been investigated using Southern blotting, PCR-based detection of deletions, and direct sequencing of exons of interest. CYP21A2 deletions were detected in 34.7% of the proband chromosomes in the CAH cohort, and 15% of those had a deletion extending into TNXB. Unique haplotypes, including three CAH probands with triplication of CYP21A2, a sibling pair with a deletion of TNXB and triplication of CYP21A2, were identified through Southern Blot analysis. A novel heterozygous 30 kB TNXB deletion that did not extend into CYP21A2 was found in a family with hypermobile form of EDS. Clinical features of patients affected by CAH and TNX deletion included situs inversus, quadrivalent aortic valve, bifid split uvula and bicorneate uterus. Clinical findings led to conclude that those with a salt-wasting form of CAH have severe developmental malformations and abnormal joint findings. Further studies, including RT-PCR and immunochemistry approach to study the TNXB expression and extracellular matrix organization, are under way to better define the clinical, molecular and biochemical aspects of this novel CAH-TNX (CAH-X) Contiguous Gene Deletion Syndrome. It represents an intersection of hereditary connective tissue disorders with an endocrine disorder.